If, by MSN, you mean MSN or Live Messenger stick with the ipod for now. Microsoft are shutting messenger down in March and transferring all their messenger users over to Skype.
If you need to use it on the laptop, go to account.live.com/password/reset and change your password for the MSN account there, then use your MSN id and new password to log in to Skype. You should find that all your contacts are already there.
The most recent version of MSN/Live Messenger is still available from places like Filehippo or Cnet but you can't get it from Microsoft any more. When you run it, it will remind you to upgrade to Skype every couple of days, but once you get past that reminder, it will work as normal.